Rusty render beads both look terrible and also produce a route into the structure for moisture. The rust is caused by the removal of the thin galvanised layer on the steel bead by the trowelling on process. This can be easily avoided by either using stainless steel or plastic beads, but these tend to be more expensive and so not specified. However, it is really worth the additional expenditure at the start.

It is still not an ideal solution though, as any corner produces a weak point as the render tends to be applied in one direction to the bead and then from the other, thus creating a tiny fracture between the layer perpendicular surfaces. It is best practice not to create this fissure and this can be achieved by rendering / plastering around a corner / angle by at least 10-20cm in one movement. Just by doing this, it removes any ‘joint’ in the material and hence improves its’ coherence. This is so important around sensitive junctions in buildings as these tend to be the weak spots in any construction.

Welsh Lime